The use of microscopy to investigate samples requires high sample quality to ensure adequate sample imaging and analytical data, including structural information and chemical compositions, are obtained. In particular, thin samples are needed in order to obtain accurate results. In order to obtain a thin enough sample, a milling device is directed onto the sample and material is removed from the sample for thinning. A known apparatus of this type includes an ion source and equipment for imaging the sample. The sample may be mounted onto a grid that is in turn mounted on a sample holder. The sample holder is adapted for insertion into a goniometer that is capable of reorienting the sample with respect to the ion source. The sample may be milled on both the top and bottom surfaces for thinning purposes, and this milling is typically a momentum transfer process in which a primary ion beam strikes the sample surface and sputters an amount of material. Alternatively, a section may be removed from the sample by way of directing the ions onto the sample at a particular angle and a given position. The goniometer and holder permit the position of the sample to be adjusted with respect to the ion beam emanating from the ion source to cause adjustment of the degree and angle of the milling of the sample. The ion beam may also be displaced with respect to the sample, including scanning or rastering across the surface of the sample. The combination of the sample holder and goniometer also serves as a vacuum seal between the processing chamber and the ambient environment.
A focused ion beam (FIB) may initially be used to mill the sample from bulk material, and the sample can be configured as a lamella. The FIB may utilize a liquid-metal ion source such as one based upon gallium or other elements. The FIB, however, utilizes a beam which is appropriate for gross sizing of the sample, but poorly adapted for fine modification of the sample which will result in electron transparency for certain imaging. The use of the FIB may therefore create detrimental aspects of the sample, such as changing crystalline material to an amorphous structure and implanting metal ions into the sample.
When a transmission electron microscope (TEM) is to be utilized to observe or analyze the sample, it is typically required that the sample be reduced to a thickness permitting electron transparency. In certain instances, a scanning electron microscope (SEM) may also require fine dimensional control of the dimensions of the sample. Unfortunately, if the sample was not milled to the required dimensions, the results obtained in the microscopic analysis will not be complete. The operator must then remove the sample from the microscopy device and place it back into the milling apparatus and remove additional material from the sample. This process may be time consuming and require guess work by the operator. However, once an operator obtains a sufficient amount of experience he or she may become proficient at determining exactly how much milling needs to be done on a particular material. Although with enough experience the operator may be capable of adequately preparing a sample for microscopic analysis, the possibility of making an error by incorrectly estimating material removal remains. Further, for novice operators, thinning samples for sensitive microscopic analysis presents certain challenges. Finally, it may be necessary to thin a number of samples in a repetitious manner with highly consistent results. It may be desired to improve accuracy, speed and consistent repeatability with which samples can be prepared for imaging and analysis. As such, there remains room for variation and improvement within the art.
Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the invention.